Method and device for the encoding and decoding of power distribution at the outputs of a system

ABSTRACT

In a method and device for the encoding/decoding of the power distribution at the outputs of a system, the distribution encoder comprises an element that receives a signal s(t) and a piece of distribution information i(t), and that superposes said piece of distribution information i(t) received on said signal s(t) received. The piece of information i(t) is used for the subsequent distribution of the total power P s  of said signal s(t) at said output or outputs {S Γ } of a system Γ. The distribution decoder comprises one or more inputs on which there is received an encoded signal c(t) or an encoded signal divided into several signal (c j (t)) jε[1,2N]  comprising the useful signal s(t) and the piece of distribution information i(t). It also comprises one or more outputs connected to the outputs {S Γ } of said system Γ to which said signal s(t) is transmitted by distributing the total power received P s  according to said piece of distribution information i(t). The disclosed method and device enable, for example, the fast, low-power switching of the outputs of a high-power system and the programming of a system with variable power outputs.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The invention relates to a method and device for the encoding/decoding of the power distribution at the outputs of a system. A possible application of the invention is the making of high-power transmitters such as for example those used by interrogators known as IFF (identification friend or foe) interrogators, using secondary radars.

[0003] 2. Description of the Prior Art

[0004]FIG. 1 shows that the current transmission chain used in IFF transmitter structures is constituted by the following elements in the following order: a driver 1, a two-channel power divider 2, a two-channel parallel amplification device 3 having an amplifier 3′ and 3″ on each channel, a two-channel recombination device 4, a circulator 5, a two-channel switching device 6 _(v) formed by PIN diodes and a transmission device 7 formed by two transmission antennas, one sum antenna Σ and one difference antenna Δ. A switching command o(t) is applied to the signal s(t) through the output switching device 6 _(v).

[0005] As can be seen in FIG. 2, the interrogation signal s(t) of an IFF transmitter has three pulses, the first and last pulse being sent by the antenna Σ and the mid-pulse being sent by the antenna Δ. In order to meet the requirements of the IFF ISLS (identification friend or foe interrogation side lobe suppression) specifications, the antenna switching between the transmission of the second gate of the interrogation signal s(t) and that of the third gate must be fast, i.e. it must be done in about some hundreds of nanoseconds (<200 ns).

[0006] It is difficult and even impossible to implement an architecture of this kind for making fast (<200 ns) power switches with a peak power of over 2 kW. Indeed, the transmission chain presently used in the making of high-power transmitters has a power switch 6 _(v) with a relatively low switching speed (with a switching time of about 1 μs). This low switching speed is actually due to the fact that it is sought to have high-power transmitters. This is because the voltage handling capability of the PIN diodes of the switch is proportional to the thickness of their intrinsic region whereas their switching speed, which is related to the lifetime of the minority carriers, is inversely proportional to this thickness. Furthermore, the standard structure of IFF transmitters dictates the use of a circulator 5 between the amplification device 3 and the switch 6 _(v) owing to an infinite standing wave ratio (SWR) which entails the use of PIN diodes having a voltage handling capability that is twice the maximum value. This means that the switching speed is further reduced.

[0007] To overcome this drawback, the present invention, instead of using a switch placed downline, uses a low-power distribution encoder, placed upline with respect to the amplification, and a distribution decoder for the selection switching of the output channels.

SUMMARY OF THE INVENTION

[0008] To this end, an object of the invention is a method for the encoding of distribution comprising a step for the superposing, on a signal s(t), of a piece of distribution information i(t) used for the subsequent distribution of the total power P_(s) of said signal s(t), appearing at output of a system Γ, to one or more outputs {S_(Γ)} of said system Γ.

[0009] This method is used by the distribution encoder comprising an element which:

[0010] receives a signal s(t),

[0011] receives a piece of distribution information i(t) used for the subsequent distribution of the total power P_(s) of said signal s(t) on said output or outputs {S_(Γ)} of a system Γ, and

[0012] superposes said piece of received distribution information i(t) on said received signal s(t).

[0013] In order to decode the distribution information, the invention also proposes a distribution decoding method comprising at least the following steps:

[0014] the reception of an encoded signal c(t) or a divided encoder signal (c_(j)(t))_(jε[1,2N]) comprising a useful signal s(t) and a piece of distribution information i(t),

[0015] the sending of said signal s(t) to each of the outputs {S_(Γ)} of a system Γ in distributing the total power P_(s) received at said outputs {S_(Γ)} depending on said distribution information i(t).

[0016] This method is used by the distribution encoder comprising:

[0017] one or more inputs at which there is received an encoded signal c(t) or a divided encoded signal (c_(j)(t))_(jε[1,2N]) comprising a useful signal s(t) and a piece of distribution information i(t) identically or differently for each signal,

[0018] several outputs connected to the outputs {S_(Γ)} of a system Γ on which said signal s(t) is sent in distributing the total power received P_(s) depending on said piece of distribution information i(t).

[0019] The invention also proposes a transmission chain comprising at least the distribution encoder and the distribution decoder described here above.

[0020] The architecture thus obtained enables the switching of the power output by improving the following parameters:

[0021] the switching speed: the switching is done in less than 300 nanoseconds;

[0022] the power handling capability of the switching function; and

[0023] the standing wave ratio (SWR) capability of the switching function which becomes infinite.

[0024] This architecture also optimizes the power balance of a transmission chain by masking the switching function losses.

[0025] Furthermore, this architecture is less complex because it enables the use of components with standard specifications commonly used in the semiconductor industry.

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Other features and advantages of the invention shall appear more clearly from the following description given by way of an example with reference to the appended figures, of which:

[0027]FIG. 1 shows an embodiment of the transmission chain with a power switch 6 _(v) placed downline according to the prior art,

[0028]FIG. 2 shows a graph of the incoming and outgoing signals of the transmission chain according to the prior art,

[0029]FIG. 3(a) shows a distribution encoder 8 according to the invention,

[0030]FIG. 3(b) shows a variant of the distribution encoder 8 according to the invention,

[0031]FIG. 4 shows a system Γ comprising a distribution encoder 8 and a distribution decoder 10 according to the invention,

[0032]FIG. 5 shows an exemplary embodiment of a system according to the invention, namely an IFF transmission chain.

MORE DETAILED DESCRIPTION

[0033]FIG. 3(a) shows an exemplary embodiment of a distribution encoder 8 according to the invention. This distribution encoder 8 has a switch 6 _(M) that receives a signal s(t) and a piece of distribution information element used to select one or more inputs of the divider 2. The divider 2, as its name indicates, divides the signal s(t) into two signals s₁(t) and s₂(t). The selection of one of the two inputs of the divider 2 by the switch 6 _(M) enables the piece of distribution information i(t) to be superposed on the signals s₁(t) and s₂(t). This superposing of this piece of distribution information i(t) on the signals s₁(t) and s₂(t) is done for example by means of a differential phase modulation between the parallel channels at output of the divider 2. The power division can then be carried out by a 3 dB/90° coupler whose properties are such that the piece of distribution information i(t) is superposed on the signal as described here above. The signals c1(t) and c2(t) resulting from this differential phase modulation comprise the signal s(t) divided in power, namely s1(t) and s2(t) which are respectively phase-shifted or not phase-shifted by 90°, depending on the input of the divider 2 at which the signal s(t) arrives, namely depending on the value of i(t).

c _(j)(t)=f _(j)(s _(j)(t),i(t)) with jε[1,2N]

[0034]FIG. 3(b) shows a variant of this distribution encoder 8 according to the invention. The distribution encoder 8 has a divider 2 which receives a signal s(t) and divides it into two signals s₁(t) and s₂(t). It is two 0°/90° phase shifters 9′ and 9″ positioned on both output channels of the divider 2 that receive the distribution information i(t) and get positioned on the value 0° or 9° for the phase-shifter 9′ and conversely on the value 90° or 0° for the phase-shifter 9″, depending on this information i(t). The resulting signals c1(t) and c2(t) are said to be differentially phase-modulated.

c _(j)(t)=g _(θj)(s _(j)(t),i(t)) with jε[1,2N] and θ _(j)ε[0°,90°]

[0035] The power divider 2 used in this case may be a 3 dB/90° coupler or a Wilkinson coupler for example. The divider 2 shown in the FIG. 3(b) is a Wilkinson coupler. If the divider 2 is a 3 dB/90° coupler, its second input is connected to a load which may be a 50-ohm load for example. However, the encoder 8 works whatever the value of this load.

[0036] The superposed distribution information i(t) thereafter enables the distribution of the total power P_(s) that arrives at the output of the system Γ on one or more outputs {S_(Γ)} of said system Γ so that the signal s(t) is sent on. This distribution information i(t) may vary continuously or discontinuously in time. The phase shifters for example may vary continuously between 0° and 90° (included) and conversely according to the value of i(t). For, the distribution information i(t) may indicate for example:

[0037] that the totality of the power P_(s) must be sent on to a single output S_(Γ) at a given instant t, or

[0038] the proportion of the power P_(s) to be sent on to each output S_(Γ) at a given instant t.

[0039] The above examples of the distribution encoder 8 are not restrictive. The divider 2 may comprise one or 2 to 2N outputs (Nε

*). The values of the angle θ_(j) are not restricted to 0° and 90° or even to the interval [0°, 90°]. The functions fj or g_(θ) _(j) may be identical on one or more channels or they may be all distinct. The superposing of the distribution information i(t) on the signal s(t) is not limited to the differential phase modulation. This superposing of the distribution information i(t) on the signal s(t) may be done by any continuous or discontinuous function using or not using a divider 2.

[0040]FIG. 4 shows an exemplary system Γ according to the invention. The distribution encoder 8 has two output channels directly or indirectly connected to the two inputs of the distribution decoder 10. If the distribution information i(t) has differentially phase-modulated the two channels at output of the distribution encoder 8, the distribution decoder 10 performs a demodulation. This demodulation is physically expressed by obtaining the sum of the power values present at the two input channels E′₁₀ and E″₁₀ of the distribution decoder 10 on either of its outputs S′₁₀ and S″₁₀ depending on the phase states on the inputs E′₁₀ and E″₁₀. The distribution decoder 10 comprises for example a 3 dB/90° coupler that demodulates the distribution information i(t). The distribution decoder generally comprises a 3 dB/n° coupler with n as an integer (3 dB/90°, 3 dB/180°, 3 dB/45°, . . . ). The phase distribution properties of 3 dB/90° couplers are known in the prior art [Anaren, RF & Microwave Components-Reference: M 1951-79, February 1997].

[0041] In general, the distribution decoder 10 receives one or more signals comprising the useful signal s(t) and the distribution information i(t). The signals received by the decoder 10 correspond to the signals sent by the encoder 8 which may or may not have undergone one or more intermediate processing operations. The distribution decoder 10 decodes and uses the distribution information i(t) to send the useful signal s(t) to one or more of the outputs {S_(Γ)} of the system Γ. It does so in distributing, depending on the decoded distribution information i(t), the total power P_(s) entering the decoder 10 at the outputs S′₁₀ and S″₁₀ of the decoder 10, each being connected to an output, S′_(Γ) and S″_(Γ) respectively of the system Γ. ${\sum\limits_{j \in {\lbrack{1,{2N}}\rbrack}}P_{E_{10}^{J}}} = {P_{s} = {\sum\limits_{1 \in {\lbrack{1,L}\rbrack}}S_{10}^{1}}}$

[0042] Since the number of output channels of the distribution encoder 8 is identical to the number of input channels of the distribution decoder 10, the number of input channels of the distribution decoder 10 is 1 or 2 to 2N (Nε

*). The number L of outputs of the distribution decoder 10 for its part is identical to that of the system Γ and is not limited (Lε

*).

[0043]FIG. 5 gives an exemplary view of a system Γ according to the invention: an IFF transmission chain. The driver 1 is followed by the distribution encoder 8 comprising for example a switch and a two-channel divider 2 (3 dB/90° coupler for example), an amplifier 3′ and 3″ on each of the two channels constituted by a high-power double transistor and then a distribution decoder 10. The driver 1 is constituted by a pulsed 500 watts C class RF transistor (with a load rate of 1%) working at 1030 MHz. The switch 6 _(M) may be of the SPDT (single-pole double-throw) type. It then uses the principle of serial PIN diode switching or the system based on λ/4 lines switched by PIN diodes whose unused output is coupled simultaneously to a resistance (50 Ohms for example). The input couplers used by the divider 2 of the distribution encoder 8 are one of the following types: 3 dB/90° hybrid ring etched on substrate, “ANAREN” (trademark) 3 dB/90° microstrip couplers; “SAGE labs” (trademark) 3 dB/90° coaxial couplers, etc. The output coupler of the distribution decoder 10 is a 3 dB/90° coupler among the types referred to here above. A circulator 5′, 5″ respectively is placed at the output S′₁₀ and S″₁₀ respectively of the distribution decoder 10. The circulator 5′ and 5″ are identical to those conventionally used in the IFF transmission chain. The transmission chain is terminated by a transmission device 7 comprising an antenna on each output channel of the distribution decoder 10 (an antenna Σ and an antenna Δ in the case of the IFF transistors).

[0044] It being known that the approximate magnitude of the power of the signal s(t) at output of the driver is 250 to 700 W, let us consider the following example in which the power of the signal s(t) observed at output of the driver 2 is 500 W. At output of the switch 6 _(M), the power obtained is about 57 dBm with a decoupling greater than 30 dB between the two outputs E′₂ and E″₂. At output of the power divider 2, whatever the input used, E′₂ or E″₂, power of 54 dBm±0.3 dB is obtained at each of the outputs S′₈ and S″₈ with a phase shift of 0°±2° or 90°±2° depending on the selected input.

[0045] The amplification device 3 consists of two transistors 3′ and 3″ in parallel giving 61 dBm±0.5 dB at output with 54 dBm at input and having a return loss of more than 15 dB at the input of each transistor. The difference between these two channels is adjusted by the setting of a variable tuning capacitor at the output of each transistor. The phase matching of the two channels thus obtained is less than 5°.

[0046] At output of the distribution decoder 10, power of 63.5 dBm±0.5 dBm is obtained at the outputs S′₁₀ or S″₁₀ with a decoupling of more than 20 dB between the two outputs.

[0047] The results of this example are validated between −40° C. and +70° C. A ±1 dB variation with respect to the nominal output power was observed.

[0048] This invention can be applied to radiofrequency (RF) transmitters having a parallel structure final power stage. However, it is not limited to radiofrequency transmitters because it can also be applied to microwave (HF) transmitters or to millimeter wave transmitters. More generally, the invention can be applied to any device requiring power switching at the outputs, for example for a space-diversity transmitter/receiver (T/R) but also to any device with variable power outputs. 

What is claimed is:
 1. A method of distribution encoding comprising a step for the superposing, on a signal s(t), of a piece of distribution information i(t) used for the subsequent distribution of the total power P_(s) of said signal s(t) appearing at output of a system Γ to one or more outputs {S_(Γ)} of said system Γ.
 2. A distribution encoding method according to the above claim comprising a step for the division of said signal s(t) into 2N signals {s_(j)(t)}_(jε[1,2N]) on 2N channels (Nε

*), this division step preceding, including or following said superposing step.
 3. A distribution encoding method according to the above claim wherein said superposing step comprises a differential phase modulation of said channels.
 4. A distribution encoding method according to one of the claims 2 or 3, wherein said division step comprises: the reception of said signal s(t), the reception of a piece of distribution information i(t), the superposing of said distribution information i(t) on said divided signals {s_(j)(t)}_(jε[1,2N]) identically or differently, the sending of the encoded signals {c_(j)(t)=f_(j)(s_(j)(t),i(t))}_(jε[1,2N]) obtained by superposing.
 5. A distribution encoding method according to the above claim comprising a switching step comprising at least the following steps: the reception of a signal s(t), the reception of the piece of distribution information i(t), the choice of one of the inputs of said division depending on the distribution information i(t), the transmission of said signal s(t) to said chosen input.
 6. A distribution encoding method according to one of the claims 2 or 3, comprising a step of phase-shifting preceded by the step of division comprising at least the following steps: the reception of the signal s_(j)(t) on each outgoing channel of the division, the reception of the piece of distribution information i(t), the phase-shifting of the signal s_(j)(t) of each channel identically or differently depending on said piece of distribution information i(t), the sending, on each channel, of the encoded signal c_(j)(t)=g_(θ) _(j) (s_(j)(t),i(t)) resulting from the phase shift.
 7. A distribution encoder comprising an element that: receives a signal s(t), receives a piece of distribution information i(t) used for the subsequent distribution of the total power P_(s) of said signal s(t) to said output or outputs {S_(Γ)} of a system Γ, and superposes said piece of received distribution information i(t) on said received signal s(t).
 8. A distribution encoder according to the preceding claim comprising a power divider (2) to divide said signal s(t) into 2N signals {s_(j)(t)}_(jε[1,2N]) on 2N channels (Nε

*), the divider comprising or being placed before or after the element performing said superposing.
 9. A distribution encoder according to the preceding claim wherein the element performing said superposing operation is a differential phase modulator of the output channels of the divider that have undergone or not undergone intermediate processing.
 10. A distribution encoder according to one of the claims 8 or 9, wherein the divider: receives said signal s(t) and said piece of distribution information i(t), and superposes said piece of distribution information i(t) on said divided signals {s_(j)(t)}_(jε[1,2N]) identically or differently, sends the encoded signals {c_(j)(t)=f_(j)(s_(j)(t),i(t))}_(jε[1,2N]) obtained.
 11. A distribution encoder of an output according to the preceding claim comprising a switch (6 _(M)) comprising at least: a first input receiving said signal s(t), a second input receiving said piece of distribution information i(t), several outputs, each output being connected to an input of said divider (2), one of said outputs sending on the received signal s(t), a device connecting the input of the switch (6 _(M)) receiving the signal s(t) to an output of the switch (6M) sending on the received signal s(t) said output being selected by the piece of distribution information i(t) received at the second input of the switch (6 _(M)).
 12. A distribution encoder according to the preceding claim, wherein: the switch (6 _(M)) is an PIN diode SPDT (single-pole double-throw) type of switch with a resistance on the unused output, and the divider has a 3 dB/90° coupler.
 13. A distribution encoder according to one of the claims 8 or 9 comprising a phase-shift device comprising, on each of the channels at output of the divider, a phase-shifter which: receives said divided signal s_(j)(t), receives said piece of distribution information i(t), phase-shifts said divided signal s_(j)(t) as a function of said piece of distribution information i(t), each channel being shifted identically or differently, sends, on each channel the encoded signal c_(j)(t)=g_(θ) _(j) (s_(j)(t),i(t)) resulting from the phase shift.
 14. A distribution encoder according to the preceding claim wherein the phase-shifters {9 ^(j)} are all-or-nothing 0°/90° phase-shifters or continuously or discontinuously varying phase-shifters.
 15. A distribution decoding method comprising at least the following steps: the reception of an encoded signal c(t) or of a divided encoded signal (c_(j)(t))_(jε[1,2N]) comprising a useful signal s(t) and a piece of distribution information i(t), the transmission of said signal s(t) to each of the outputs {S_(Γ)} of a system Γ by distributing the total power received P_(s) on said outputs {S_(Γ)} depending on said piece of distribution information i(t).
 16. A distribution decoder comprising: one or more inputs on which there is received an encoded signal c(t) or a divided encoded signal (c_(j)(t))_(jε[1,2N]) comprising a useful signal s(t) and a piece of distribution information i(t) identically or differently for each signal, several outputs connected to the outputs {S_(Γ)} of a system Γ to which said signal s(t) is transmitted by distributing the total power received P_(s) depending on said piece of distribution information i(t).
 17. A distribution decoder comprising: one or more inputs on which there is received an encoded signal c(t) or a divided encoded signal (c_(j)(t))_(jε[1,2N]) comprising a useful signal s(t) phase-shifted by a piece of distribution information i(t), several outputs connected to the outputs {S_(Γ)} of a system Γ on which said signal s(t) is sent in distributing the total power P_(s) received according to the phase state, of the received signal or signals, that is generated by the piece of distribution information i(t).
 18. A distribution encoder according to one of the claims 16 or 17, comprising a 3 dB/9° coupler.
 19. A transmission chain comprising at least one distribution encoder according to one of the claims 7 to 14 and one distribution decoder according to one of the claims 16 to
 18. 20. A transmission chain according to the preceding claim, comprising at least one of the following devices: a driver, upline from the distribution encoder, an amplification device comprising an amplifier on each channel between the distribution encoder and the distribution decoder, a circulator on each channel downline from the distribution decoder, a transmission device comprising a transmission antenna on each channel downline from the decoding distributor, each constituting one of the outputs S_(Γ).
 21. A transmission chain according to the preceding claim wherein: the driver comprises a radiofrequency or microwave or millimetrical transistor, and each amplifier comprises a high-power transistor, the sending device comprises a sum antenna (Σ) and a difference antenna (Δ). 